Among the adsorbents permitting good separation of nitrogen and oxygen contained in air, lithium zeolites and particularly lithium faujasites are particularly efficacious by reason of their increased selectivity of the adsorption of nitrogen relative to oxygen.
The principal drawback of these zeolites is nevertheless their very high cost.
In the prior art, lithium faujasites are prepared by ion exchange with synthetic sodium faujasites, which are available commercially.
More particularly, the methods described foresee the treatment of sodium faujasites by solutions of lithium salts. However, to the extent that faujasites, like most zeolites, have a better affinity for Na.sup.+ ions than for Li.sup.+ ions, a large part of the sodium salts solutions must be poured over the faujasite so as to produce a faujasite exchanged with at least 80% lithium. On the average, the consumption of lithium ions corresponds to 4 to 12 times the quantity of lithium ions to be incorporated in the faujasite. However, the lithium salts used, principally chlorides, are cumbersome and pollutant: these major drawbacks have until now limited the development and use of lithium zeolites.
So as to overcome these drawbacks, the use of recycling techniques for the residual solutions of lithium salts from lithium zeolite production units would be desirable.